1680s, "aware of one's action," a word of the English Enlightenment (Locke was using it by 1690), from self- + conscious. Morbid sense of "preoccupied with one's own personality" is attested from 1834 (in J.S. Mill). Related: Self-consciously; self-consciousness.

in reference to things, "to destroy itself automatically," from self- + destruct, apparently first attested in the U.S. television series "Mission Impossible" (1966). Self-destructive is recorded from 1650s, and self-destruction "suicide" is attested from 1580s.

[Self-interest] is a doctrine not very lofty, but clear and sure. It does not seek to attain great objects; but it attains those it aims for without too much effort. ... [It] does not produce great devotion; but it suggests little sacrifices each day; by itself it cannot make a man virtuous; but it forms a multitude of citizens who are regulated, temperate, moderate, farsighted, masters of themselves; and if it does not lead directly to virtue through the will, it brings them near to it insensibly through habits. [Alexis de Tocqueville, "Democracy in America"]